A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
In a factory, commonly referred to as a “fab” or “foundry”, in which semiconductor devices are manufactured, each lithographic apparatus is commonly grouped with a “track” comprising wafer handling devices and pre- and post-processing devices to form a “lithocell”. The processing devices of the track may include chiller plates for cooling substrates, bake plates for heating substrates, spin coaters for coating substrates, e.g. with resist, developers and a substrate handler, or robot, for moving substrates between the various devices within the track and substrate load and unload ports of the lithographic apparatus. The devices in the track are used to prepare the substrate for the lithographic exposure process (for example, coating the substrate) and to finish the lithographic process (for example, developing the substrate) and so the substrates must be transferable between the track and the lithographic apparatus. These devices are generally referred to collectively as the track.
Substrates, such as wafers, which may be blank or have already been processed to include one or more process or device layers, are delivered to the lithocell in lots (also referred to as batches) for processing. The lot size may be arbitrary or determined by the size of carrier used to transport substrates around the fab between different process apparatuses, metrology apparatuses (which can include inspection apparatuses) or storage locations.
Substrates are typically moved within the track and between the lithographic apparatus and the track by one or more robot arms in the track, one robot arm being capable of reaching beyond the confines of the track to, for example, the load and unload ports of the lithographic apparatus. There are also configurations in which the transfer robot is located in the lithographic apparatus instead of the track. The configuration of the track and lithographic apparatus can therefore be either an in-line configuration, where one end of the track is aligned with one end of the lithographic apparatus; or an orthogonal configuration, where the track is placed perpendicularly to the lithographic apparatus, depending on the reach of the robot arm and the position of the load port of the lithographic apparatus. Because the configurations of the lithocell are limited, lithographic apparatus sizes are limited, as is the packing density of such lithocells in a fab. Furthermore, older fabs are designed for older lithocells that print on small substrates (typically 200 mm in diameter). Because of the limited configurations, it is difficult to replace older lithocells with newer lithocells that accommodate bigger substrates (for example, 300 mm).